1. Field of the Invention
The present invention relates to a liquid crystal display device, and in particular relates to a liquid crystal display device in which misalignment between upper and lower substrates is suppressed.
2. Description of the Related Art
A liquid crystal display device has a configuration that a thin-film transistor (TFT) substrate in which a pixel electrode, a TFT and the like are formed in a matrix, and an opposite substrate in which a color filter and the like are formed at a position corresponding to that of the pixel electrode of the TFT substrate are arranged with a predetermined gap therebetween, and liquid crystal is retained in the gap between the TFT substrate and the opposite substrate. To regulate the gap between the TFT substrate and the opposite substrate to be constant, a columnar spacer is interposed between the substrates.
In a liquid crystal display device, when a temperature change occurs between upper and lower substrates due to a use environment condition or lighting of a backlight, because rates of thermal expansion of the upper and lower substrates are different, misalignment of one substrate to another substrate in a surface direction occurs, and a display failure occurs due to occurrence of uneven brightness caused by misalignment between a pixel region of the upper substrate and a pixel region of the lower substrate and a bright spot caused by shaving of an orientation film associated with the misalignment in a surface direction. In particular, when a screen size is large or thickness of polarizing plates laminated on the upper and lower substrates are different, misalignment between the upper and lower substrates in a surface direction becomes more significant.
About regulation of an interval between substrates and prevention of misalignment between upper and lower substrates, Japanese Patent Application Laid-Open Publication No. 2003-131238 discloses that columnar spacers having different height are formed on one substrate, reduction of a frictional resistance between the substrate and an opposite substrate is attempted with a taller spacer, and a cell gap between the substrates is finally ensured with a shorter spacer.
Japanese Patent Application Laid-Open Publication No. 2003-84290 discloses a liquid crystal display device in which a columnar spacer for maintaining a substrate gap is arranged in a pixel electrode at a contact portion that supplies electrical signals to the pixel electrode to realize stable control of a panel gap without impairing display quality and an aperture ratio of pixels.
Also, Japanese Patent Application Laid-Open Publication No. 2003-5190 discloses that to suppress a variation in inter-substrate positions and a cell gap caused by a positional variation of a columnar spacer due to application of an external force, a top part of the columnar spacer formed fixedly at an inner surface of one of a pair of substrates is positioned at a concave part of a multilayer structure film of another substrate.